A note on the flow regimes in the unsteady, rectilinear flow of a perfect gas

Homentropic, unsteady, rectilinear flows can be classified in (i) constant flows, (ii) simple waves, (iii) general flows. After a short discussion of this standard theory, an attempt is discussed to extend this scheme to non-homentropic flows. The principal result is that a flow with the constraint du+(1/a) dp=0 everywhere is physically impossible. In two final sections two suggestions are discussed to remedy the situation, and the linearized case is discussed where analogous features are present.     

The method of matched asymptotic expansions for the periodic solution of the van der pol equation

The purpose of this paper is to apply the method of intermediate matching for connecting the four local asymptotic solutions of the Van der Pol equation, given by Dorodnicyn [1]. It turns out that for the approximation of the periodic solution a fifth local solution is needed. The present approach results in a reduction of the computational work. The amplitude of the periodic solution is determined up to a higher order accuracy in v than has been done so far.     

Ten-deg off-axis test for shear properties in fiber composites

A combined theoretical and experimental investigation was conducted to assess the suitability of the 10-deg off-axis tensile-test specimen for the intralaminar-shear characterization of unidirectional composites. Composite mechanics, a combined-stress failure criterion and a finiteelement analysis were used to determine theoretically the stress-strain variation across the specimen width and the relative stress and strain magnitudes at the 10-deg plane. Strain gages were used to measure the strain variation across the specimen width at specimen midlength and near the end tabs. Specimens from Mod-I/epoxy. T-300/epoxy, and S-glass/epoxy were used in the experimental program. It was found that the 10-deg off-axis tensile-test specimen is suitable for intralaminar-shear characterization and it, is recommended that it should be considered as a possible standard test specimen for such a characterization.     

Étude du comportement viscoélastique du polycarbonate de bisphénol-A partiellement cristallisé

Résumé On étudie dans cet article un procédé pour obtenir des polycarbonates de bisphénol-A de divers taux de cristallinité. On détermine la variation thermique du module-(10 sec) et la résistance au choc des ces polymères. On étudie également l'influence du recuit sur les propriétés mécaniques.

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Summary This paper describes a procedure to obtain polycarbonate of bisphenol A samples of various degrees of crystallinity. The modulus-temperature curves and the impact strength of these materials are investigated. The results show the importance of the annealing procedure on the mechanical properties of these systems.

     

Integrated-plane photoelastic method—Application of photoelastic isodynes

It has been shown by Pindera and Mazurkiewicz that a new type of scattered-light modulation in the plane of a two-dimensional photoelastic object can be obtained when the stationary integrated photoelastic method developed by Pindera and Straka is applied in a scanning mode and when the transfer function of the photoelastic system satisfies certain conditions. The new type of light modulation, called field of isodynes by the authors, carries information on stress components normal to the direction of propagation of primary beam, and on corresponding total-force component. The points where this stress component is equal to zero can be easily determined. The classical scattered-light modulation along a chosen line represents a cross section of a corresponding isodynes field. It is shown that these features of the method of isodynes make it possible to easily determine the distribution and values of normal stress components at any arbitrary rectilinear cross section, and to check immediately the accuracy of measurements. The experimental determination of contact stresses and contact regions using the method of isodynes is especially simple and elegant.     

Potentiostat for use in electro-chemical experiments

Summary In many electro-chemical experiments it is desirable that one of the current-carrying electrodes of an electrolytic bath has a constant potential. This may be realized by manual control of the bath current. Owing to the sudden and unpredictable potential fluctuations of the electrode concerned, this is very difficult and even impossible in some special cases, e.g. when passivating an Fe-electrode in aqueous H₂SO₄. In addition there may be a considerable time-lag between the potential and the current fluctuations. The different types of potentiostats described so far seem to have too large a time-lag or/and too low a sensitivity for this purpose. The authors describe a potentiostat with proportional and integrating properties resulting in a stabilization of the potential within 1/2 mV in favourable sections of the potential current characteristic. Even with an electrode with a very steep potential current characteristic (e.g. the above mentioned Fe-electrode) the ripple never exceeds a few mV. The bath current, the maximum value of which is 30 mA, is the differential current of two electronic tubes. This type of circuit offers various advantages.     

Measurements on a molecular beam apparatus for mass spectrometric study of reactions in flames

Summary The formation of a molecular beam in sampling 1 torr to 1 atm. gases (Ar or H₂) is studied for three diameters of the sampling orifice. To modulate the beam, use is made of a mechanical chopper placed very near the sampling orifice. This enables us to measure the scattering of the beam by collisions between beam molecules. From our measurements it follows that these collisions are very important for >0.020 mm at an initial pressure of 1 atm. We discuss the consequences of our results for mass spectrometric studies of flames.     

Approximate analytical solutions for solute transport in two-layer porous media

Mathematical models for transport in layered media are important for investigating how restricting layers affect rates of solute migration in soil profiles; they may also improve the analysis of solute displacement experiments. This study reports an (approximate) analytical solution for solute transport during steady-state flow in a two-layer medium requiring continuity of solute fluxes and resident concentrations at the interface. The solutions were derived with Laplace transformations making use of the binomial theorem. Results based on this solution were found to be in relatively good agreement with those obtained using numerical inversion of the Laplace transform. An expression for the flux-averaged concentration in the second layer was also obtained. Zero- and first-order approximations for the solute distribution in the second layer were derived for a thin first layer representing a water film or crust on top of the medium. These thin-layer approximations did not perform as well as the binomial solution, except for the first-order approximation when the Peclet number,P, of the first layer, was low (P<5). Results of this study indicate that the ordering of two layers will affect the predicted breakthrough curves at the outlet of the medium. The two-layer solution was used to illustrate the effects of dispersion in the inlet or outlet reservoirs using previously published data on apparatus-induced dispersion.The U.S. Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged.